Answered by Shaykh Faraz A. Khan
Question: Some people object to saying ‘Salam’ and say we should say ‘Assalamu alaikum’ and not ‘Salam’ as it is against the sunna, but can you inform me whether there is a Quranic basis for saying the short form ‘Salam’?
Answer: Assalamu alaikum wa rahmatullah,
I pray this finds you in the best of health and states.
The well-known sunna is to say ‘Assalamu alalikum’, with the definite particle ‘al-‘ at the beginning (which transforms to as-).
It would suffice to use the indefinite form ‘Salam alaikum’, but using the definite particle ‘al-‘ is superior. Some scholars mention that this is because ‘Assalamu alaikum’ (with the definite particle) is the appropriate greeting for this life, while the indefinite ‘Salam[un] alaikum’ (as found in many Qur’anic verses) will be the greetings in Paradise, such as in the verse, “Perpetual peace be upon you (Salam[un] alaikum) for your having been patient — so what a great final abode!” (13:24) [Kuwaiti Fiqh Encyclopedia]
As for verses in which the indefinite ‘Salam[un]’ is used in this life, such as in the conversation of Ibrahim (peace be upon him) with his guests who were angels, there are rhetorical reasons why that form is most appropriate in those particular verses, which therefore do not serve as a basis of the ideal way of our greeting one another.
And Allah knows best.
Checked & Approved by Faraz Rabbani